Surrey Police said the suspect, who they did not name, was detained on suspicion of conspiracy to commit murder.

He was held at an address in Chessington at around 7:30am “and is currently in police custody where he will be interviewed”.

Mr Al-Hilli’s brother Zaid Hilli, who is in his 50s and lives in Surrey, has previously denied any feud with his sibling over an inheritance.

Surrey Police set up a Joint Investigation Team to work with French police on solving the brutal murders.

The al-Hillis’ four-year-old daughter Zeena lay undiscovered under her mother’s corpse in their BMW for eight hours after the shooting, while her seven-year-old sister Zainab was found with serious injures after being shot and beaten.

Surrey police said today’s arrest was pre-planned and the result of on-going inquiries.